Optical encoder based fader design

ABSTRACT

An apparatus indicating the position of an adjustable lever, such as a control lever in a digital audio console, is described. A frame member constrains movement of the adjustable lever. The lever is operatively connected to an encoder apparatus, such that movement of the lever causes movement of the encoder apparatus to provide an indication of position of the lever within the frame member.

FIELD OF THE INVENTION

This invention relates to digitally-based apparatus for indicating theposition of a adjustable member, such as a fader control lever, whichmay be used in an apparatus to control the gain or other parameter of anaudio or other signal.

BACKGROUND OF THE INVENTION

Audio faders are well-known in the prior art and are used to adjust thegain of one or more audio signals in the production of a recording of asequence of audio events. A common prior art apparatus for controllingthe gain of the audio signal includes a movable control lever, slider orknob (collectively referred to hereinafter as a "lever") which isconnected to a linear potentiometer. Movement of the lever, usually in aone-dimensional, linear movement, changes the electrical characteristicsof the potentiometer. The potentiometer is electrically connected bywell known techniques across a voltage supply having a magnituderepresenting the range over which it is desired to vary the controlsignal applied to the control input of an associated voltage controlledamplifier (VCA), also well known in the prior art.

Generally, in this type of prior art device, the potentiometer has itswiper arm connected directly to a fader control lever in order to vary aparameter such as the gain of an audio signal. In use, the operatormanually adjusts the position of the lever which is coupled to the wiperarm of the potentiometer. This action adjusts the control voltageapplied to the gain control input of the voltage controlled amplifier.Such a prior art analog potentiometer system is described in U.S. Pat.No. 4,429,219, issued Jan. 31, 1984 to Yochum et al. A problemassociated with prior art mechanically-based potentiometers, accordingto the description given in the Yochum et al. patent (col. 3, lines15-23), is that rubbing of the lever's wiper arm within the linearpotentiometer causes the mechanical assembly to wear, and this in turnintroduces noise into the gain control signal provided at the wiper arm.The noise produced by the potentiometer is combined with the audiosignal entering the voltage-controlled amplifier. Consequently, the gaincontrol operation introduces an undesired noise component into the audiosignal, causing audio signal inaccuracies and distortions.

Today, a transition from analog-based audio processing consoles todigital-based consoles for audio mixing and recording applications isoccurring. Accordingly, in order to use the prior art analogpotentiometer type of fader control discussed above, analog to digitalconverters are necessary to convert the analog position signal from thepotentiometer and its related lever to a digital signal, thus addingmore circuitry and adding a potential for further errors and noise inthe system.

Therefore, it is desirable to utilize in digital-based audio consoles adigitally-based audio fader system. The Yochum et al. patent describedabove, as well as U.S. Pat. No. 4,412,182 issued Oct. 25, 1983 toYochum, disclose audio fader systems which do not rely on mechanicalcontact between the elements for establishing the position detectionoperation. Instead, a shutter and light beam arrangement is employedwhich is described in the Yochum et al. patent (col. 4, lines 50-57) asbeing essentially immune to the wear problems associated with the priorart analog potentiometer system. Furthermore, the bulk of the signalprocessing may be accomplished with digital circuitry permitting,according to the Yochum et al. patent, low noise operation. In theYochum et al. patent, a number of light emitting diodes or light sourcesare interfaced with a shutter-like device or other obturator and aphoto-sensitive detector. As disclosed in the Yochum et al. patent,there are 13 emitter/detector pairs and thus 13 signals whose valuescollectively identify the location of the shutter over the range of 66possible positions (col. 7, lines 6-18). The shutter is connecteddirectly to a manually movable lever.

The prior art also includes a rotatable fader knob attached directly tothe shaft of an optical encoder, such that rotation of the knob rotatesthe optical encoder shaft, which, with appropriate circuitry, controlsthe gain, for example, of an audio signal.

Other light-based position or channel detection and selection apparatusis shown in the following patents: U.S. Pat. No. 4,015,253 issued Mar.29, 1977 to Goldstein; U.S. Pat. No. 4,137,451 issued Jan. 30, 1979 toEinolf; U.S. Pat. No. 4,122,395 issued Oct. 24, 1978 to Schotz et al.;U.S. Pat. No. 3,835,384 issued Sep. 10, 1974 to Liff; U.S. Pat. No.3,755,681 issued Aug. 28, 1973 to Montross; U.S. Pat. No. 3,381,288issued Apr. 30, 1968 to Van Vlodrop; U.S. Pat. No. 3,619,626 issued Nov.9, 1971 to Rudolph; U.S. Pat. No. 4,573,110 issued Feb. 25, 1986 toDrumm; and U.S. Pat. No. 3,363,106 issued Jan. 9, 1968 to Park.

The apparatus described in the Yochum et al. patent, while perhaps animprovement over the prior art analog contact-type potentiometer system,has certain drawbacks and disadvantages. For example, the systemrequires a number of light-emitting elements and light-detectingelements, specifically 13 emitter/detector pairs, which will produce 13digital signals whose values must be interfaced in order to provide asignal which corresponds to a value of the movable lever in any one of anumber of positions (col. 7, lines 6-18).

In addition, the Yochum et al. patent does not disclose any means bywhich the lever may be automatically moved to a selected position,although this type of mechanism is well known in the audio fader priorart. In these devices, in further editing of an audio sequence, thefader lever or levers are caused to move to the position(s) the operatorhad adjusted them to during previous mixing or editing passes in orderthat the operator may visually observe the previous positioning(s) ofthe fader levers. This acts as a visual indication to the operator andassists him/her in adjusting and further editing the audio sequence.Thus, while the Yochum et al. patent broadly discloses an apparatuswhich may be seen as a logical extension from an analog audio fader to adigital audio fader, the apparatus described in the Yochum et al. patenthas the disadvantages set forth above. What is desirable, therefore, isa system which is digitally-based, but has few parts, provides goodtactile feedback to an operator, is accurate and allows for automaticmovement of the fader lever knob.

SUMMARY OF THE INVENTION

Thus, it is a general object of the present invention to provide anapparatus for digitally indicating and altering the position of amovable member, in the preferred embodiment illustrated as an audiofader lever.

Furthermore, it is another object of the present invention to provide animproved apparatus for indicating the position of a fader lever usingoptical encoder technology for precision and to reduce wearcharacteristics present in prior art potentiometer-based systems.

It is yet another object of the present invention to provide anapparatus which does not materially degrade in operation or accuracyover time as compared to the prior art devices discussed above.

It is still another object of the present invention to provide acontrollable motor system connected to the optical encoder-based faderof the present invention to automatically move the fader lever toprevious editing pass positions.

In accordance with the present invention, an apparatus is provided forindicating the position of a movable member and more particularly amovable lever controlling a parameter in an audio or other controlsystem. The apparatus includes a frame which supports the lever knob.The lever knob is constrained to move in one-dimensional linear space bya number of rails or other suitable members. The frame, which forms partof the present apparatus, also includes a rotary optical encoder of atype in which the amount and direction of rotation of the shaft of theoptical encoder corresponds to the position of the lever within itsconstrained area of linear movement. The lever is attached to theoptical encoder by a suitable taut wire, string or other elongated meansso that linear movements of the lever are translated into rotationalmovements of the optical encoder.

In addition, a motor may be incorporated in and mechanically associatedwith the apparatus. The purpose of the motor is to automatically movethe lever to the position(s) to which the operator previously set theslider during previous mixing or editing operations. Therefore, theposition of the lever translates into a visual feedback-type indicationto the operator, in an audio editing environment, of the amount of gainwhich was applied to a signal during previous audio mixing or editingoperations or, more generally, to the changes in previous operations ofthe lever knob.

Finally, while the preferred embodiment utilizes the present inventionin a digital audio apparatus, it has applications in other fields aswell, including lighting applications, video editing applications,industrial processing equipment or any other apparatus which can utilizea variable, digitally-controlled signal and associated lever knob.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and advantages will become readilyapparent from the detailed description below taken in conjunction withthe accompanying drawing where:

FIG. 1 is a frontal view of a fader control in accordance with thedisclosure of the present invention and illustrates the relativepositioning of the motor, the lever and encoder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the preferred embodiment of the present apparatus. Asseen in FIG. 1, a fader apparatus 10 includes a frame 12. Frame 12 isshown as having an upper frame portion 13 and two depending andextending end frame members 15 and 17. Frame members 15 and 17 supporttwo rails 14 and 16. While two rails 14 and 16 are shown in FIG. 1, anynumber less than or more than the two rails shown may be utilized asdesired. The main purpose of the rails is to constrain movement of leverbody 18 to linear movements. Lever body 18 is shown as having arectangular form (but may have any other suitable form). Rails 14 and 16pass through apertures 8 and 9 in the lever body 18.

As shown in FIG. 1, the rails 14 and 16 are located one above the otherwithin the frame 12. If desired, the rails may be located closertogether, further apart or in a parallel side-by-side position asdesired to support the lever body and constrain its movement to thetranslational directions shown by arrow 19 and thus prevent any movementin directions perpendicular to directions 19. The lever body 18 haslever knob 20 attached to it, shown for illustrative purposes only in asimple form. It is well-known in the art that a rounded or other shapeknob may be utilized. The lever knob 20 rides within a slot 30 formed inthe frame portion 13 of the fader apparatus 10. The slot acts toconstrain movement of the lever knob 20 to the directions 19 and alsoserves to help prevent dirt or dust from entering into the area wherethe rails 14 and 16 and the lever body 18 are located. An opticalencoder 22, which is shown as being of a rotary type, is attached to thefader apparatus 10 at one portion 15 of the frame 12. In the opticalencoder of a rotary type illustrated, a pulley 25 is attached to therotatable shaft of the encoder. The rotatable shaft conventionally has arotatable code wheel or disc mounted thereon, a light source (which maybe a LED) on one side of the code wheel or disc, a photo detectionassembly on the other side of the code wheel or disc and signalprocessing circuitry. For each encoder rotation position in eitherdirection of rotation, there is produced a differential binary output sothat rotatable shaft position can be absolutely determined, based on theamount of light from the light source passing through the code wheel ordisc to the photo detection assembly. The structure and operation ofoptical encoders is described in "Input/Output Devices", Machine Design,Jun. 1990, p. 389 et seq. While a number of different types of encodersmay be utilized, one suitable optical encoder is Model RE20F which isavailable from the Copal Company of Japan.

In the present invention, the lever knob 20 is operatively connected tothe optical encoder 22 such that movement of the knob will cause thepulley 25 attached to the shaft of the optical encoder 22 to rotate. Asillustrated in FIG. 1, this is accomplished through the use of a tautstring, wire or other elongated material 24 which is attached at 27 bysuitable means (such as a screw, rivet or glue) to the lever knob 20 andis wrapped around the shaft of the pulley 25. A second pulley is alsopreferably used and a spring, elastic or other suitable means may beutilized to maintain the elongated material taut. This second pulley 29,shown mounted on a shaft, is located on the opposite side of the firstpulley 25 from the lever knob 20. The string or other elongated material24 is wrapped around the shaft of the pulley 29 as well. Thus, as can beseen in FIG. 1, movement of the lever knob in either of lineardirections 19 will cause the pulley 25 to rotate due to the frictionalinteraction between the string 24 and the pulley 25. The amount ofrotation is in proportion to the position of the lever knob 20 withinthe slot 30. Electrical cable 28 is connected between encoder 22, bysuitable means well-known to those skilled in the art, to a computerapparatus 32. The circuit board 32 may be incorporated within or atleast operatively connected to a computer 35, which itself may becontained within a known digital audio console. A number of digitalaudio consoles are commercially available. One such digital audioconsole is manufactured by the assignee of the present invention. Thecomputer 35 may, however, be associated with any number of othernon-audio devices, depending on the use to which the lever knob is put,such as in digitally controlling lighting, video editing or otherprocesses. The circuit board 32 will receive and translate electricalsignals generated from rotation of the pulley 25 of the optical encoder22. The counts and direction of the counts are then translated intopositional movements which indicate the position of the lever knob 20within the slot 30. The translation of the signals will, in turn, betransformed into other analog or digital signals which will adjust anynumber of parameters, for example in the preferred embodiment, the gainon an audio signal operatively connected to the audio fader.

The functioning and operation of the circuit board 32 will now bediscussed. Circuit board 32 includes a number of elements, including aprogrammable logic array (PAL) 50. PAL 50 accepts the electrical countsignals from encoder 25 through cabling 28, and translates that digitalinformation and forwards it to the microprocessor 52, which oversees theoperation of signals form the PAL 50 and performs other processing andstoring functions. A random access memory (RAM) 54 may be utilized tostore operating programs for microprocessors 52 and store counts fromencoder 22 and PAL 50. The purpose of the digital-to-analog convertor(DAC) 56 will be explained below. The circuit board 32 is shown in FIG.1 as being operatively connected to computer 35 which may be containedwithin or otherwise associated with a digital audio console.

Although a taut string or wire is shown in FIG. 1, other well-knownmeans which translate lateral motion to rotational motion may be used,such as a rod attached to the lever knob 20 which will rub against andmove the optical encoder pulley 25 or a gearing system using a circulargear on the pulley 25 and a lateral gear attached to the lever knob 20.Although a rotatable encoder has been illustrated and discussed, othertype encoders, such as a linear encoder, may be utilized as well, and beattached to the taut string or wire by suitable means, not shown butwell known in the art, which translate movement of the lever knob 20 tomovement of a linear encoder. The pulley 29 may be free-standing or may,as shown in FIG. 1, be attached to motor 26. Motor 26, in turn, isattached through electrical cabling 34 to the digital audio console 32.

In audio mixing and editing operations, the operator may desire to viewthe position(s) of one or more levers during a previous editing ormixing operation as explained above. During the mixing or editingoperation, the operator will move the lever knob 20 to effect, forexample, a change in the audio gain of the signal which is associatedwith that particular lever knob. It is well understood that any numberof lever knobs may be used to edit and mix any number of audio signals.The editing or mixing operation for a particular audio sequenceconnected with a particular lever knob may, through the use of theoptical encoder disclosed above, be stored internal to or external tothe audio console 32. The "replay" of a previous editing or mixingsequence causes movement of the lever knob, providing an importantvisual feedback to the operator of the previous adjustment(s) which hadbeen made to an audio sequence.

To achieve this "replay" effect within the apparatus of the presentinvention, the motor 26 is described above (which is connected bycabling 34 to the circuit board 32) I activated, as described below. Asmentioned earlier, the RAM 54 (or other suitable solid state ordisk-based memory) stores a count of the position of the lever 20position(s) prior to a "replay". When the operator desires the operatorto "replay" a particular positioning of a particular lever knob, theoperator causes, by well known means, the counts stores on circuit board32 to be fed to the DAC 56 which will convert the digital signals toanalog signals the motor 35 understands through cable 34. Uponcommencement of "replay", the motor 26 will rotate the pulley 29 causingthe slider knob to move within the slot 30, thus providing the operatorwith a visual indication of the previous audio editing operationsthrough the use of the so-called "moving fader". An additional featureof the present invention is the provision of suitable means such that,when an operator touches the lever knob 20 during the "replay" operationjust described, the lever knob may halt all further movement within theslot 30. This may subsequently cause the audio console 32 to overridethe previously recorded audio editing or mixing sequence, as is wellknown in the art. The means to stop the motor 26 may be accomplished ina number of ways, including, in a manner a well-known in the art,utilizing the microprocessor 52 to sense a change in capacitance in theapparatus of the present invention when an operator touches the lever.The capacitance change when an operator touches the lever is thus sensedby the microprocessor. This sensing is operable only in severalautomation modes well known in the art, including the "replay" mode,such that any touching of the lever knob would cause the motor 26 toshut down. In operation, a cable 58 in FIG. 1 is connected utilizingwell known techniques between the lever knob 20 and PAL 50. Touching ofthe lever knob is sensed by the microprocessor 52, through cable 58 andPAL 50. This in turn causes microprocessor 52 to signal DAC 56 to turnoff current flowing through cable 34 to motor 26. Other techniques, suchas employing a known type of microswitch on the lever knob may also beutilized to cause motor 26 to be turned off. Other methods of achievinga halt of the movement of the lever knob are well known to those skilledin the art. While an electrical motor 26 has been described herein, itis to be understood that other means to achieve movement of the leverknob are feasible. These include linear or rotational electromagneticcoil actuators and other electrical, electromagnetic andelectromechanical devices which convert a given amount of electricalcurrent to movement of a shaft, arm or other mechanical actuator.

Thus, an improved fader design has been described above which does awaywith the noise and analog signal discrepancies which may occur in theuse of the prior art potentiometer type fader systems while providing asimpler, more accurate, virtually noise-free digital-based system whichallows the operator to accurately position and determine the degree ofaudio gain and other audio mixing parameters. It is more accurate andnoise-free because it eliminates the mechanical wear which is present inconventional mechanically-based potentiometer designs. Furthermore, thelever and pulley design has been found by the inventor to provide asmoothness in operation and general good tactile "feedback" compared toprior art potentiometer designs, as well as being less expensive tomanufacture. The good tactile "feel" and "feedback" of the apparatus ofthe present invention is important because good tactile feedback is verydesirable for acceptance of the present invention by a professionaloperator. It provides a uniform amount of frictional resistance tomovement of the control lever, yet is not too tight or too loose anddoes not "hang-up" as may be the case prior art systems. This aspect ofthe present invention was, to the inventor's knowledge, never addressedby the prior art devices.

Furthermore, while in the embodiment illustrated the optical faderapparatus is utilized to control audio signals, the apparatus of thepresent invention may be utilized to control other parameters andsources, such as light sources in a well known type of lighting console.In both audio and lighting consoles, a number of fader control levers,ranging from as few as 1 or 4 such levers to hundreds of levers (butgenerally in the range of 48-64 levers) may be utilized. The costsavings discussed above are multiplied by the number of levers utilizedin a particular audio or lighting console. This is accomplished in anapparatus which is simple to construct and tends to virtually eliminatewear associated with prior art potentiometer-based fader systems.

Thus, other sources and parameters which may be controlled using thepresent invention include lighting controllers, industrial processcontrollers, video mixing consoles and other applications in which apotentiometer formerly served to control a changeable parameter.

Given the embodiments of the invention described herein, it should beapparent to those skilled in the art that the foregoing is merelyillustrative and not limiting, having been presented by way of exampleonly. Numerous modifications and other embodiments are within the scopeof one of ordinary skill in the art and are contemplated as fallingwithin the scope of the invention as defined by the appended claims.

What is claimed is:
 1. Apparatus for indicating the position of a memberwith respect to another member, comprising:a frame member; a linearlymovable member positionable and movable within the frame member; adigital encoding apparatus operatively connected to the frame member,the encoder being responsive to linear movement of the movable member togenerate an electrical signal indicative of the degree of movement; and,means for connecting the movable member and the encoding apparatus,movement of the movable member causing movement of the encodingapparatus, whereby the amount and direction of movement of the encoderis related to the position of the movable member within the framemember, wherein the movable member is an audio fader control lever andthe apparatus is an apparatus to control the gain of an audio signal. 2.Apparatus for indicating the position of a member with respect toanother member, comprising:a frame member; a linearly movable memberpositionable and movable within the frame member; a digital encodingapparatus operatively connected to the frame member, the encoder beingresponsive to linear movement of the movable member to generate anelectrical signal indicative of the degree of movement; and, means forconnecting the movable member and the encoding apparatus, movement ofthe movable member causing movement of the encoding apparatus, wherebythe amount and direction of movement of the encoder is related to theposition of the movable member within the frame member, wherein theframe member further comprises frame legs extending from opposite endsof the frame member, the movable member being movable within anelongated slot and having an extending block with at least one apertureformed therein, and at least one elongated shaft parallel to theelongated slot and extending from one frame leg to the other frame legthrough the aperture of the extending block, whereby the movable memberis constrained to move along the elongated shaft and within theelongated slot.
 3. Apparatus for indicating the position of a memberwith respect to another member, comprising:a frame member; a linearlymovable member positionable and movable within the frame member; adigital encoding apparatus operatively connected to the frame member,the encoder being responsive to linear movement of the movable member togenerate an electrical signal indicative of the degree of movement; and,means for connecting the movable member and the encoding apparatus,movement of the movable member causing movement of the encodingapparatus, whereby the amount and direction of movement of the encoderis related to the position of the movable member within the framemember, wherein the digital encoding apparatus is a rotatable apparatus,and wherein the amount and direction of rotation of the rotatableencoder is indicative of the position of the movable member within theframe member, in which the means for connecting is an elongated memberattached to the movable member, the elongated member being in frictionalengagement with a portion of the encoding apparatus, whereby movement ofthe movable member causes rotation of the encoding apparatus furthercomprising an electrical motor operatively connected to the elongatedframe, a source of electrical current for causing a shaft containedwithin the motor to rotate, and a pulley attached to the shaft, thestring-like member being wrapped around the electrical motor pulley,such that when electrical current is applied to the motor under controlof a digital computing apparatus, the shaft rotates, rotating the pulleyand moving the movable member attached to the string-like member withinthe frame member and the pulley attached to the encoding apparatus. 4.Apparatus for indicating the position of a member with respect toanother member, comprising:a frame member; a linearly movable memberpositionable and movable within the frame member; a digital encodingapparatus operatively connected to the frame member, the encoder beingresponsive to linear movement of the movable member to generate anelectrical signal indicative of the degree of movement; and, means forconnecting the movable member and the encoding apparatus, movement ofthe movable member causing movement of the encoding apparatus, wherebythe amount and direction of movement of the encoder is related to theposition of the movable member within the frame member, wherein thedigital encoding apparatus is a rotatable apparatus, and wherein theamount and direction of rotation of the rotatable encoder is indicativeof the position of the movable member within the frame member, in whichthe means for connecting is an elongated member attached to the movablemember, the elongated member being in frictional engagement with aportion of the encoding apparatus, whereby movement of the movablemember causes rotation of the encoding apparatus further comprising anelectrically-controlled motivation means for moving the movable member,a source of electrical current for causing the motivation means to move,the motivation means being connected to the movable member, such thatwhen current is applied to the motivation means, the movable member ismoved by the motivation means.
 5. The apparatus of claim 3, wherein thedigital computing apparatus is a digital audio apparatus.
 6. Theapparatus of claim 1, wherein the movable member further comprises alevel knob adapted for gripping by an operator to position the movablemember within the frame member.
 7. The apparatus of claim 1, furthercomprising an electrical conductor connected to the encoding apparatus,and wherein the encoding apparatus, upon rotation, sends an electricalsignal on the electrical conductor to a digital computing apparatusoperatively connected to the electrical conductor to produce anindication of the position of the movable member within the framemember.
 8. The apparatus of claim 7, in which the digital computingapparatus includes a means for receiving and processing the electricalsignal from the encoding apparatus.
 9. The apparatus of claim 3, inwhich an electrical conductor is attached between the motor and adigital computing apparatus, the digital computing apparatus including ameans for receiving and processing electrical signals from the encodingapparatus, further comprising means for causing the motor to rotate tomove the movable member within the frame member.
 10. The apparatus ofclaim 9, further comprising a means associated with the movable memberfor sensing touching by an operator, an electrical conductor connectedto the means for sensing and to the digital computing apparatus, wherebysensing of touching causes the digital computing apparatus to activate aselected function.
 11. The apparatus of claim 10, wherein sensing oftouching of the movable member causes the digital computing apparatus tocause the motor to stop rotation, halting movement of the movablemember.
 12. The apparatus of claim 10, wherein the means for sensinginclude the operation of the digital computing apparatus to sense thechange in capacitance when an operator touches the movable member.